1. Field of the Invention
This invention relates in general to well casing handling equipment, and in particular to well casing elevators and spiders.
2. Description of the Prior Art
In a typical derrick arrangement, a traveling block is suspended from the derrick crown block by a series of cables, which are driven by the derrick drawworks to raise and lower the traveling block along the vertical axis of the derrick. The usual derrick hook is suspended from the traveling block and supports an elevator by means of links. When handling casing, slip-type elevators are used. Such elevators have a tapered interior bowl and a series of gripping slips, which are pivotally moved up and down within the bowl to grip the exterior surface of the casing being handled.
A casing spider rests on the derrick floor and supports the casing string in the well bore by means of slips, which are set to grip the casing exterior. A new joint of casing is raised into position over the well bore by the casing elevator, and the lower end of the casing joint is connected to the upper end of the casing string in the well bore. The elevator is then stripped down over the top of the casing joint and the slips are set to grip the casing exterior. The elevator is then used to lift the casing string, releasing the slips of the lower spider, and the casing string is lowered into the well bore. The slips of the spider are then set to support the casing string in the well bore, and the elevator is disengaged and stripped upward and off of the casing to allow another casing joint to be moved into position. This cycle is repeated until all of the casing is run in the well bore.
Elevator/spiders are powerful, double-duty tools designed to handle long, heavy casing strings. These tools are convertible and can be used either as casing spiders or as elevators. Often, when handling casing strings, these tools will be used in tandem, utilizing one tool as a casing spider and the other tool as an elevator.
Elevator/spiders generally have slips which are pivotally operable between an upper, retracted position and a lower, gripping position. The slips are moved between the upper and lower positions by means of fluid cylinders. In a typical arrangement, a yoke is connected to the slips by suitable linkages. The yoke pivots about a pivot axis in the approximate center of the yoke when the fluid pressure is applied to the cylinders. During normal raising or lowering of the slips, the fluid cylinders serve to retain the slips in the upper or lower position. The rate of raising or lowering the slips can be controlled by providing an adjustable air flow valve in the air distribution system leading to the fluid cylinders.
Elevator/spiders also typically have a locking mechanism to lock the slips in the upper, retracted position. If the slips should fall to the lower gripping position while pipe is being raised or lowered through the elevator/spider, the movement of the pipe would be impeded and damage may occur to the drilling equipment. Mechanical locking mechanisms in the prior art are susceptible to the jarring and vibration which occurs on a typical drilling platform. Therefore, there was a need to provide a more reliable locking mechanism for the elevator/spider.